In comparison to magnetic storage devices, nonvolatile semiconductor memory has higher power consumption and higher performance, and is also more expensive. Nonvolatile semiconductor memory may, for example, include NAND type flash memory. In recent years, together with the advances in semiconductor technology, the cost of nonvolatile semiconductor memory is decreasing, and it has been drawing attention as a mainstream storage device to replace hard disk drives (HDDs).
Flash memory may include a plurality of memory cells (hereinafter abbreviated as “cells”) for storing data. In addition to cells capable of storing 1-bit information (referred to as SLC), there are also cells capable of storing information of 2-bits or more (referred to as MLC; in addition, cells capable of storing information of 3-bits or more may be referred to as TLC). When MLC-type cells are used in flash memory, the bit cost can be reduced in comparison with cases that use SLC-type cells. Further, by utilizing cells capable of storing information of 3-bits or more (TLC) among MLC-type cells, it is possible to further reduce the bit cost in comparison with using cells capable of storing 2-bit information.
Also, in recent years, techniques have been proposed that make it possible to change the amount of information (number of bits) that can be stored in a cell. For example, Patent Document 1 discloses memory that can set a particular area to operate in a mode in which 1 bit of data can be written in one memory cell transistor, and set another area to operate in a mode in which multiple bits of data can be written.